| Carbon dioxide capture and storage technology (CCS) is one of the most important methods to achieve CO2emission reduction and promote the clean utilization of fossil energy technology. The CCS methodologies comprise three steps:CO2capture, CO2transportation and CO2storage, in which, CO2capture is the most costly and energy intensive. Adsorption is a promising CO2capture techniques that could be less costly and energy efficient, and it overcomes the disadvantages of traditional liquid amine-based absorption processes, including solvent degradation, equipment corrosion, and foaming in the gas-liquid interface. However, the traditional porous adsorbents generally can not adapt to the actual industrial conditions of flue gas, such as big amount, high CO2concentration and complex components. Therefore, in this work, a kind of molecularly imprinted CO2adsorbent, with high CO2capacity and selectivity was developed by bulk polymerization, and experimental researches on CO2adsorption and desorption from coal-fired flue gas were carried out. The main research contents and conclusions are as follows.According to the mechanism of molecular imprinting technique, three elements of molecularly imprinted CO2adsorbent, template, functional monomer and cross-linker, were determined to be ethanedioic acid, acrylamide, and ethylene glycol dimethacrylate based on the properties of coal-fired flue gas, such as high CO2content, harsh operation condition and complex flue gas composition. The molecularly imprinted CO2adsorbent was prepared by bulk polymerization. The N2adsorption and thermo-gravimetric analysis were used to investigate the effect of solvent and initiation reaction on the structure of adsorbent, the results showed that the acetonitrile solvent system and thermal-initiation reaction were benefit for the high surface area of adsorbent. The3D model of adsorbent established by Chembio3D and the CO2capture experiments verified the rationality of CO2capture by molecularly imprinted CO2adsorbent.The relationship between the structure of molecularly imprinted CO2adsorbent and its CO2adsorption property, the regeneration properties and the effect of other flue gas components on CO2adsorption property were investigated deeply in this paper. The structure of adsorbents was characterized by N2adsorption experiment, thermo-gravimetric analysis, Fourier transform infrared spectroscopy and SEM analysis. The CO2adsorption capacities and adsorption enthalpies were investigated by DSC-TGA experiments. The regeneration and the effect of other flue gas components were studied by fix-bed experiments. The results showed that the CO2capacity of molecularly imprinted CO2adsorbent was increased with the surface area and the amide group density. The highest CO2adsorption capacity was0.912mmol/g at25℃, and0.478mmol/g at 60℃. The CO2adsorption capacity only reduced by2%after50adsorption-desorption cycles. The adsorption enthalpy was below40kJ/mol, which is in the range of the enthalpy of physical-sorption. The calculated separation factors of CO2/N2reached up to260, and the CO2adsorption property was nearly not affected by of H2O, O2and NOx in flue gas, suggesting that the adsorption selectivity was great. The CO2adsorption property varied with the SO2concentration, when the SO2concentration was lower than150mg/m3, the CO2capacity would be promoted with its increase; but when it was lower than150mg/m3, the CO2capacity would be reduced with its increase. The regeneration experiments showed that the SO2adsorption was reversible.In order to solve the problems brought by bulk polymerization, including bad controllability of grinding, hard elution of template, and inhomogeneity of imprinting sites, a kind of surface imprinting CO2adsorbent was prepared using silica gel as the substrate material, and compared with the other three modified silica gel adsorbents, which were respectively grafted with (3-aminopropyl) trimethoxysilane, grafted with acrylamide polymer, and impregnated with acrylamide polymer. The results showed that all modified silica adsorbents displayed good thermal-stability in the temperature range of25-250℃. Surface imprinting CO2adsorbent with the highest amide density and surface area showed the highest CO2capacity, which was1.03mmol/g at25℃and0.67mmol/g at60℃. The CO2adsorption enthalpy of surface imprinting adsorbent was in the range of the of physical-sorption enthalpy. The regeneration characteristics of the surface imprinting CO2adsorbent were investigated by fix-bed experiments, and the results showed that it can be completely regenerated at70℃, the CO2capacity showed no obvious drop after50adsorption-desorption cycles. A breakthrough model was successfully developed to describe the breakthrough process under different adsorption temperature, CO2concentration, and gas flow rate, and the mass transfer coefficients of CO2were calculated from the breakthrough model, the results showed that adsorption rate could be promoted by increasing temperature, flow rate and CO2concentration, among which the effect of gas flow rate is the most obvious. |
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